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From: moriko@hh.iij4u.or.jp
References: <20011205.231421.74752105.moriko@mizuki.noe.mcu.or.jp>
	<20011210.201214.68561659.moriko@saorin.noe.mcu.or.jp>
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$B?9$G$9!#4XO"(B RFC $B$rFI$_$^$7$?!#(B($B%Q%1%C%H$bFI$_$^$7$?(B)

>   1. $B%U%i%0%a%s%H2=$5$l$J$$$h$&$K$9$k(B (set mtu max 1414 $B$^$G2<$2$k(B)

$B:rF|$3$&=q$$$?$N$G$9$,!"$h$/8+$?$i%U%i%0%a%s%H2=$5$l$F$$$^$7$?!#(B

$B$^$?!"(BRFC 1323 $B$O(B MSS $B$N%5%$%:$KL54X78$J%*%W%7%g%s$G$9$N$G!"(B

  sysctl -w net.inet.tcp.rfc1323=0

$B$GDL?.2DG=$K$J$C$?$N$OC1$K(B TCP $B%X%C%@$ND9$5$,C;$/$J$C$?$+$i$N$h$&$G$9!#(B

$B4Q;!$7$?7k2L!"$=$b$=$b(B mss $B$K@_Dj$7$F$$$kCM$,JQ$J$N$G$O$J$$$+$H(B
$B;W$C$F(B ppp(8) $B$N%=!<%9$rD4$Y$F$_$k$H!":GBg(B mss $B$N7W;;$K0J2<$N(B
$B%^%/%m$,Dj5A$5$l$F$$$^$7$?!#(B

  /usr/src/usr.sbin/ppp/tcpmss.c:
  #define MAXMSS(mtu) (mtu - sizeof(struct ip) - sizeof(struct tcphdr))

$B$3$3$G(B sizeof (struct tcphdr) $B$O(B option filed $B$r4^$s$G$$$J$$$N$G(B
20 octet $B$H$J$k$h$&$G$9!#(B

MSS $B$O(B RFC 879 $B$K$h$l$P(B

      MSS = MTU - sizeof(TCPHDR) - sizeof(IPHDR)

$B$G$"$j!":G0-$G(B

      MSS = MTU - 60 - 60 = MTU - 120

$B$@$H$5$l$F$$$^$9!#F1;~$K0J2<$N$h$&$J5-=R$b$"$j$^$9$,!"(BRFC 1323 $B$H$+$,(B
$B$=$N8e=P$F$$$k$N$G!">/$J$/$H$b:G>.$N(B 20 octet $B$H2>Dj$9$k$N$O(B
$B8=:_$G$O$^$:$$$G$7$g$&!#(B

   The moderate position assumes the that the IP is maximum size (60
   octets) and the TCP header is minimum size (20 octets), because there
   are no TCP header options currently defined that would normally be
   sent at the same time as data segments.

$B$H$$$&$o$1$G!"(Bppp(8) $B$r=$@5$9$l$P$h$$!"$H$$$&$N$,7kO@$K$J$k$H;W$&$N$G$9$,!"(B
$B4*0c$$$H$+$"$C$?$i65$($F2<$5$$!#$9$0$K$O;n$;$^$;$s$,!";n$7$FLdBj$J$1$l$P(B
send-pr $B$7$h$&$H;W$$$^$9!#(B

-- 
$B?9(B $B9@Fs(B	(MORI Kouji)
E-mail: moriko@hh.iij4u.or.jp
